1. Field of the Invention
The invention relates to a computer tomography device, including
an X-ray source, PA1 an X-ray detection system for picking up a number of density profiles of an object to be radiologically examined, PA1 a reconstruction unit for deriving an image signal from the density profiles, and PA1 a control system for adjusting the X-ray source on the basis of a density value of the object. This invention also relates to a method of computer tomography.
2. Description of the Related Art
A computer tomography device of this kind is known from United States patent U.S. Pat. No. 5,400,378.
The control system of the known computer tomography device adjusts the tube current of the X-ray source on the basis of relative X-ray absorption values derived from "scout data". The "scout data" represent the attenuation of X-rays in the object relative to a standard value. Such scout data comprises the minimum values of two density profiles picked up by exposing the object to be examined to X-rays from two mutually perpendicular directions. The tube current is adjusted on the basis of the relative X-ray absorption values. In the known computer tomography device the adjustment of the X-ray source is adapted to the relative X-ray absorption in the part of the object to be examined, for example a patient to be radiologically examined. However, the control system does not suitably take into account the fact that the desired image quality differs for images of different parts of the object to be examined.
The density profiles are picked up by irradiating the patient by means of X-rays from a number of directions. An image of, for example a cross-section of the object is reconstructed from the density profiles. The operation of the known computer tomography device is also known from the general article "X-ray computed tomography for medical imaging" by Harish P. Hiriyannaiah in IEEE Signal Processing Magazine, March 1997, pp. 42-59.